The Guardian by Cristin Harber

Falling in love would end Jason Green’s clandestine career. That was okay; he’d planned to quit anyway. There was no better time than after proposing to Roxana Carter. But Jason hadn’t expected his employer to refuse his resignation unless he left in a body bag.
Roxana loved many things about her man. The stability he offered after years of family tragedies was at the top of her list. Then again, his killer bedroom moves were also a strong contender for the number one spot. Ranking their relationship qualities was the most challenging part of her life until the arrival of a mysterious gun-wielding couple.
Their message offered a shattering revelation. Roxana’s steadfast man isn’t who he seems.